Simple ramps are widely used to ease passage between two sites at different elevations. Ramps provide both a continuous surface and a mechanical advantage to ease the movement of heavy loads and vehicles including wheelchairs.
Unfortunately, many sites present challenges to installing a simple ramp. For example, some site pairs lie close together on the plane but at significantly different elevations. In such cases, a simple ramp might have an uncomfortably steep incline that is difficult to traverse. Ramps linking a boat dock to the shore present a particular challenge because the ramp incline varies continuously, and often widely, with changing water level. Similarly, ramps linking a terminal to ships, airplanes, trucks, or other vessels must be readjusted to the position and elevation appropriate for each such vessel.
A number of more complicated powered devices and systems have been proposed to help move people or materials between two sites while maintaining the people or materials in their natural orientation, unaffected by ramp incline.
For example, U.S. Pat. No. 4,026,388, granted to Denis C. Creissels on May 31, 1977 for an "Inclined Lift," describes a horizontal platform that is winched along an inclined track. The Creissels system suffers from a number of disadvantages. Most importantly, whenever the track incline is changed, the platform must be readjusted to preserve its horizontal orientation. The Creissels system is therefore not well suited for variable-incline uses such as at a boat dock. A second disadvantage is that the winch mechanism renders the system essentially an elevator and therefore necessitates the attendant rigorous safety inspections. A simple ramp is generally not considered to present the same safety concerns as an elevator.
U.S. Pat. No. 4,280,593, granted to W. Michael Moore for a "Diagonal Elevator," describes a system in which a conventional elevator winch and counterweight mechanism drives an elevator cage through diagonal guides or tracks. The cage travels along an inclined path but is so adjusted within the tracks as to have a horizontal orientation at all times. Clearly, however, the Moore system suffers from the same disadvantages as were mentioned for the Creissels system.
U.S. Pat. No. 4,821,845, granted on Apr. 18, 1989 to Guy De Viaris for a "Traversing Elevator," discloses a winch and track system for carrying an elevator cage through a continuous series of vertical, diagonal, and horizontal translations, all the while maintaining the cage in a horizontal orientation. The De Viaris system is intriguing; however, it again suffers from similar disadvantages to the Creissels system.
Canadian Patent Application No. 2,171,665, filed by John Edward Ratcliff and Robin Vincent Baker on Mar. 13, 1996 for "Improvements In Platform Lifts," discloses a platform supported on the coupler link of a planar four-bar linkage. The four-bar linkage is shaped as a parallelogram and the frame link is maintained in a horizontal orientation. As the crank and driven links pivot in parallel under the power of a ram, the coupler link, and therefore the platform, are translated through an inclined path, all the while maintaining a horizontal orientation in parallel to the frame link. While the Ratcliff et al. system recognizes the symmetry of the parallelogram, it has significant disadvantages. Structural and material limitations restrict the size and therefore the travel of the four-bar linkage. Further, the mechanism is relatively complex and would likely require the same kind of careful safety inspections as the previously described systems.
What is needed is a ramp system for guiding people and materials through an incline while maintaining them in their natural orientation, unaffected by the incline. The present invention is directed to such a system.